It is well known to provide a valve of the butterfly valve type in which a disc is supported on a diametrically extending shaft or shafts in a circular bore of a valve housing. Various efforts have been made to provide gaskets and seals to prevent or at least inhibit flow of the valved medium when the valve is in its closed position, i.e., leakage.
A valve of this general type is shown in U.S. Pat. No. 2,385,510 which includes structure at the transitions between rings concentric to the support shafts and the gasket ring disposed in a peripheral groove on the pivoted valve member such that a complete seal between the pivotable valve, the shaft and the bearing for the shaft is not possible, leading to losses through leakage of the flowing medium.
In a butterfly valve shown in U.S. Pat. No. 3,526,385, an attempt is made to improve the sealing action by disposal of cylindrical parts on the rings of the seal concentric to the shaft. The cylindrical parts lie in recesses of the pivotable valve member so that the periphery of the cylindrical part is against the valve and the inner part thereof is against the shaft. Improvement is possible with this structure to a limited degree only when a soft sealing raw material is used and the production tolerances of the parts is kept small.
Also, the insertion of a gasket ring with cylindrical parts to the grooves and recesses of the pivoting member requires an elastic or soft sealing material which is, therefore, not wear-resistant because of the decreased inside diameter, that material being exposed to wear as a result of the valve member movement.